U.S. patent application number 13/256287 was filed with the patent office on 2012-01-12 for photobiological measuring device and analyzing method.
This patent application is currently assigned to Shimadzu Corporation. Invention is credited to Akihiro Ishikawa.
Application Number | 20120010484 13/256287 |
Document ID | / |
Family ID | 42739493 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120010484 |
Kind Code |
A1 |
Ishikawa; Akihiro |
January 12, 2012 |
PHOTOBIOLOGICAL MEASURING DEVICE AND ANALYZING METHOD
Abstract
A photobiological measuring device has a computing unit
generating an unwanted component removal observation signal by
removing the signal corresponding to the unwanted component from an
observation signal. The computing unit is provided with: a mixing
matrix making unit for separating observation signals into the
products of a mixing matrix and independent component signals
through independent component analysis; a power spectrum computing
unit generating transformed independent component signals, which
are functions of frequency and intensity, by Fourier transforming
the independent component signals, which are functions of time and
intensity, and computing power spectra in predetermined frequency
bands of transformed independent component signals; and an unwanted
component signal determining unit detecting the independent
component signal corresponding to the unwanted component from among
the independent component signals by comparing the power spectrum
in a predetermined frequency band of each transformed independent
component signal with a threshold.
Inventors: |
Ishikawa; Akihiro; (Kyoto,
JP) |
Assignee: |
Shimadzu Corporation
Kyoto
JP
|
Family ID: |
42739493 |
Appl. No.: |
13/256287 |
Filed: |
January 12, 2010 |
PCT Filed: |
January 12, 2010 |
PCT NO: |
PCT/JP2010/050205 |
371 Date: |
September 13, 2011 |
Current U.S.
Class: |
600/310 |
Current CPC
Class: |
A61B 5/0042 20130101;
A61B 2562/0233 20130101; A61B 5/7257 20130101; A61B 5/14553
20130101; A61B 2562/046 20130101 |
Class at
Publication: |
600/310 |
International
Class: |
A61B 5/1455 20060101
A61B005/1455 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2009 |
JP |
2009-068351 |
Claims
1. A photobiological measuring device, comprising: a light
transmitting/receiving unit having a number of light transmitting
probes to be provided on the surface of the skin of a subject and a
number of light receiving probes to be provided on the surface of
the skin; a light transmitting/receiving unit control unit
acquiring an observation signal indicating chronological variations
concerning a portion to be measured in a subject by allowing said
light transmitting probes to irradiate the surface of the skin with
light while controlling said light receiving probes in order to
detect light emitted from the surface of the skin; and a computing
unit generating an unwanted component removal observation signal by
removing the signal corresponding to the unwanted component from
said observation signal, wherein said computing unit comprises: a
mixing matrix making unit separating observation signals into the
products of a mixing matrix and independent component signals
through independent component analysis; a power spectrum computing
unit generating transformed independent component signals, which
are functions of frequency and intensity, by Fourier transforming
the independent component signals, which are functions of time and
intensity, and thus computing power spectra in predetermined
frequency bands of the transformed independent component signals;
and an unwanted component signal determining unit detecting the
independent component signal corresponding to the unwanted
component from among the independent component signals by comparing
the power spectrum in a predetermined frequency band of each
transformed independent component signal with a threshold,
2. The photobiological measuring device according to claim 1,
wherein said computing unit comprises: an unwanted component
removal mixing matrix making unit making an unwanted component
removal mixing matrix in which 0 is substituted for the column
vector corresponding to an unwanted component in said mixing matrix
on the basis of the independent component signal corresponding to
an unwanted component found in said unwanted component signal
determining unit; and an unwanted component removal observation
signal generating unit generating unwanted component removal
observation signals by multiplying an unwanted component removal
mixing matrix with independent component signals.
3. The photobiological measuring device according to claim 1,
wherein said predetermined frequency band is at least one frequency
band selected from the group consisting of a frequency band
indicating the blood flow in the skin, a frequency band indicating
fluctuations in the heart rate, and a frequency band indicating
pulsation or respiration.
4. An analysis method for generating an unwanted component removal
observation signal by removing the signal corresponding to an
unwanted component from an observation signal using a
photobiological measuring device comprising: a light
transmitting/receiving unit having a number of light transmitting
probes to be provided on the surface of the skin of a subject and a
number of light receiving probes to be provided on the surface of
the skin; and a light transmitting/receiving unit control unit
acquiring an observation signal indicating chronological variations
concerning a portion to be measured in a subject by allowing said
light transmitting probes to irradiate the surface of the skin with
light while controlling said light receiving probes in order to
detect light emitted from the surface of the skin, the analysis
method being characterized by comprising: a mixing matrix making
step of separating observation signals into the products of a
mixing matrix and independent component signals through independent
component analysis; and a unwanted component signal determining
step of finding the independent component signal corresponding to
an unwanted component from among independent component signals by
comparing the power spectrum in a predetermined frequency band in
each transformed independent component signal with a threshold.
Description
CROSS REFERENCE TO PRIOR APPLICATIONS
[0001] This application is a U.S. National Phase application under
35 U.S.C. .sctn.371 of International Application No.
PCT/JP2010/050205, filed on Jan. 12, 2010 and claims benefit of
priority to Japanese Patent Application No. 2009-068351, filed on
Mar. 19, 2009. The International Application was published in
Japanese on Sep. 23, 2010 as WO 2010/106826 A1 under PCT Article
21(2). All of these applications are herein incorporated by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a photobiological measuring
device and analyzing method for acquiring an observation signal
which indicates variations chronologically in terms of a portion to
be measured using light, and in particular to an optical
encephalographic device for measuring the function of a portion of
the brain in a non-invasive manner using near-infrared rays (fNIRS:
functional near-infrared spectroscope), or an oxygen monitor for
monitoring the amount of oxygen consumption in the portion to be
measured in a living body.
BACKGROUND
[0003] A photobiological measuring method for measuring the inside
of a living body easily and in a non-invasive manner through the
fact that the concentration of hemoglobin corresponds to the oxygen
metabolizing function inside the living body has been known.
According to this photobiological measuring method, the
concentration of hemoglobin is found from the amount of light that
transmits through a living body when the living body is irradiated
with light of which the wavelength ranges from the visible light
region to the near-infrared region. Furthermore, hemoglobin
combines with oxygen to form oxyhemoglobin or separates from oxygen
to form deoxyhemoglobin. It is also known that within a brain,
oxygen is supplied to the activated portions through the blood flow
redistribution function so that the concentration of oxyhemoglobin
increases as a result of the combination with oxygen. Therefore,
brain activity can be monitored by measuring the concentration of
oxyhemoglobin. Oxyhemoglobin and deoxyhemoglobin have different
spectral absorbing properties in the region ranging from visible
light to near-infrared rays, and therefore the concentration of
oxyhemoglobin and the concentration of deoxyhemoglobin can be
respectively found using near-infrared rays having two different
wavelengths (for example, 780 nm and 850 nm).
[0004] Thus, a light measuring device with a holder (light
transmitting/receiving unit) having a number of light transmitting
probes and a number of light receiving probes has been developed
(see Japanese Unexamined Patent Publication 2006-109964). The light
measuring device allows the brain to be irradiated with
near-infrared rays by means of the light transmitting probes
provided on the surface of the scalp of a subject, and at the same
time detects the amount of near-infrared rays emitted from the
brain by means of the light receiving probes provided on the
surface of the scalp. In addition, the light transmitting probes
and the light receiving probes are inserted into through holes
provided in the holder so that the distances (channels) between the
light transmitting probes and the light receiving probes are
constant, and the light detection signal (amount of light) can be
gained from a number of portions of the brain at a certain depth
from the surface of the scalp.
[0005] FIG. 2 is a plan diagram showing the positional
relationships between 16 light transmitting probes and 16 light
receiving probes in a holder. The light transmitting probes 12 and
the light receiving probes 13 are arranged in a tetragonal lattice
structure so as to alternate both in the row and column directions
in the holder 11. The holder 11 is designed by taking the distance
between the scalp and the brain into consideration, and when the
subject is an adult, the distance (channel) between the light
transmitting probes 12 and the light receiving probes 13 is 30 mm.
When the channel is 30 mm, it is possible for the light detection
signal to be gained from the location at a depth of 15 mm to 20 mm
from the middle point in the channel. That is to say, the location
at a depth of 15 mm to 20 mm from the surface of the scalp
corresponds approximately to a portion on the surface of the brain,
and thus 52 light detection signals indicating chronological
variations can be gained in terms of 52 portions on the surface of
the brain (#1 to #52). Though light emitted from the light
transmitting probes 12 can be detected by distant light receiving
probes 13 other than the adjacent light receiving probes 13, it is
assumed that in order to simplify the description, only the
adjacent light receiving probes 13 can detect the light.
[0006] On the basis of the thus-gained 52 light detection signals,
the concentration of oxyhemoglobin (observation signals) in 52
portions on the surface of the brain (#1 to #52) X.sub.n(t) (n=1, 2
. . . 52), the concentration of deoxyhemoglobin (observation
signals) and the total concentration of hemoglobin (observation
signal), which is calculated from these, can be found. FIG. 3 is a
diagram showing a monitor screen of the photobiological measuring
device displaying the 52 concentrations of oxyhemoglobin X.sub.n(t)
(#1 to #52). Here, the longitudinal axis for each observation
signal X.sub.n(t) indicates the concentration of oxyhemoglobin and
the lateral axis indicates time t.
[0007] Incidentally, the 52 displayed observation signals
X.sub.n(t) in FIG. 3 consist of overlapping signals on the basis of
fluctuations in the blood flow through the skin and the heart rate
as well as variations in pulsation and respiration, in addition to
signals on the basis of the blood flow variations according to the
brain functions.
[0008] Thus, the observer, such as a doctor, makes a sharp
distinction visually between the signal on the basis of the blood
flow according to the brain function in the observation signal
X.sub.n(t) and other signals so that the observer can easily
diagnose whether or not there is a condition, such as cerebral
ischemia. For example, only the signal that is in sync with the
brain's task is handled as a brain function signal, or a signal
that is difficult to be regarded as a physiological change within
the brain is handled as an artifact. Furthermore, random noise is
removed through an integration process with a great number of
repeated measurements.
[0009] According to another method for easily diagnosing whether or
not there is a condition such as cerebral ischemia, the observation
signal X.sub.n(t) is statistically analyzed using a linear model
(GLM), and the result is compared with the reference observation
signal so that the similarity between the reference observation
signal and the observation signal X.sub.n(t) as well as the
evaluation of statistical significance (value P) can be calculated
as the statistical result (see Japanese Unexamined Patent
Publication 2003-265442).
[0010] When the brain function of a subject is measured with a
movement such as walking provided as a task is measured visually as
described above, the heart rate changes and the signal on the basis
of the change in the blood flow in the skin is also in sync with
the task. Therefore, when only the signal that is in sync with the
task is handled as the brain function signal, in some cases it
cannot be precisely diagnosed whether or not there is a condition
such as cerebral ischemia.
[0011] Though the statistical analysis as described above makes it
possible to find the similarity and the evaluation (value P)
concerning the observation signal X.sub.n(t), in some cases it
cannot be precisely diagnosed whether or not there is a condition
such as cerebral ischemia because signals on the basis of
fluctuations in the blood flow in the skin and the heart rate as
well as variations in pulsation and respiration in addition to the
signals on the basis of the blood flow according to the brain
functions keep overlapping the observation signal X.sub.n(t).
[0012] Thus, an example provides a photobiological measuring device
and analyzing method according to which the signal corresponding to
an unwanted component can be removed from the observation
signal.
SUMMARY
[0013] The photobiological measuring device according to the
present example, has: a light transmitting/receiving unit having a
number of light transmitting probes to be provided on the surface
of the skin of a subject and a number of light receiving probes to
be provided on the surface of the skin; a light
transmitting/receiving unit control unit for acquiring an
observation signal indicating chronological variations concerning a
portion to be measured in a subject by allowing the above described
light transmitting probes to irradiate the surface of the skin with
light while controlling the above described light receiving probes
in order to detect light emitted from the surface of the skin; and
a computing unit for generating an unwanted component removal
observation signal by removing the signal corresponding to the
unwanted component from the above described observation signal,
wherein the above described computing unit has: a mixing matrix
making unit for separating observation signals into the products of
a mixing matrix and independent component signals through
independent component analysis; a power spectrum computing unit for
generating transformed independent component signals, which are
functions of frequency and intensity, by Fourier transforming the
independent component signals, which are functions of time and
intensity, and thus computing power spectra in predetermined
frequency bands of the transformed independent component signals;
and an unwanted component signal determining unit for detecting the
independent component signal corresponding to the unwanted
component from among the independent component signals by comparing
the power spectrum in a predetermined frequency band of each
transformed independent component signal with a threshold.
[0014] Here, the "observation signal" may be a light detection
signal that is detected by light receiving probes or the
concentration of oxyhemoglobin, the concentration of
deoxyhemoglobin or the total concentration of hemoglobin, which are
calculated from the light detection signal.
[0015] In addition, the "signal corresponding to an unwanted
component" can refer to a signal other than the signal on the basis
of the blood flow according to the brain function and is the signal
on the basis of the blood flow in the skin, the signal on the basis
of the fluctuations in the heart rate, and the signal on the basis
of pulsation or respiration, for example.
[0016] Furthermore, the "predetermined frequency band" refers to
any frequency band that can be set in advance, and the frequency
band indicating the blood flow in the skin (0.03 Hz to 0.15 Hz),
the frequency band indicating the fluctuations in the heart rate
(0.15 Hz to 0.5 Hz), and the frequency band indicating pulsation or
respiration (0.8 Hz to 2.0 Hz) can be set as the "predetermined
frequency band," for example.
[0017] In the photobiological measuring device according to the
present example, the light transmitting/receiving control unit
allows the light transmitting probes to irradiate the surface of
the skin with light and control the light receiving probes in order
to detect light emitted from the surface of the skin, and thus N
observation signals X.sub.n(t) concerning N portions to be measured
can be acquired. Here, the observation signals X.sub.n(t) consist
of overlapping signals on the basis of the fluctuations in the
blood flow in the skin and the heart rate as well as variations in
pulsation and respiration, in addition to signals on the basis of
the blood flow according to the brain functions.
[0018] The computing unit removes the signal corresponding to an
unwanted component from the observation signals X.sub.n(t). First,
as shown by the following formula (1), the mixing matrix making
unit separates the N observation signals X.sub.n(t) into the
products of an N.times.N mixing matrix and N independent component
signals S.sub.n(t) through independent component analysis
(ICA).
[ Formula 1 ] ( X 1 ( t ) X 2 ( t ) X n ( t ) ) Observation Signal
= ( a 11 a 12 a 1 n a 21 a 22 a 2 n a n 1 a n 2 a nn ) Mixing
Matrix ( S 1 ( t ) S 2 ( t ) S n ( t ) ) Component Signal
Independent ( 1 ) ##EQU00001##
[0019] Here, the column vector in the mixing matrix indicates the
weight of a certain independent component signal S.sub.n(t) in a
portion to be measured. That is to say, the observation signals
X.sub.n(t) are a linear combination of the N independent component
signals S.sub.n(t) from independent sources for generating signals
with each element in the mixing matrix as a weight coefficient.
[0020] In the case where there is a signal source for a signal on
the basis of the blood flow in the skin, which is irrelevant of the
signal on the basis of the blood flow according to the brain
function, it is possible for some of the N independent component
signals S.sub.n(t) to be the signal on the basis of the blood flow
in the skin from the signal source.
[0021] It is generally known that signals on the basis of the blood
flow in the skin appear in a predetermined frequency band
.lamda..sub.1. Therefore, in order to find out the independent
component signal S.sub.n(t) corresponding to an unwanted component
from among the N independent component signals S.sub.n(t), the
power spectrum computing unit Fourier transforms the N independent
component signals S.sub.n(t) so as to generate N transformed
independent component signals S.sub.n(.lamda.). Thus, the power
spectrum computing unit calculates the power spectrum
S.sub.n(.lamda..sub.1) of the predetermined frequency band
.lamda..sub.1 in the N transformed independent component signal
S.sub.n(.lamda.).
[0022] Next, the unwanted component signal determining unit
compares the N power spectra S.sub.n(.lamda..sub.1) with the
respective thresholds T so as to find the independent component
signal S.sub.n(t) corresponding to an unwanted component from among
the N independent component signals S.sub.n(t). In the case where
the power spectrum S.sub.1(.lamda..sub.1) is not less than the
threshold T, for example, the independent component signal
S.sub.1(t) is determined to be the signal corresponding to an
unwanted component. Meanwhile, in the case where the power spectrum
S.sub.1(.lamda..sub.1) is less than the threshold T, the
independent component signal S.sub.1(t) is determined to be a
signal on the basis of the blood flow according to the brain
function. Here, the number of signals that are determined to
correspond to an unwanted component is not necessarily one, but may
be plural.
Effects of the Invention
[0023] As described above, the photobiological measuring device can
remove the signals corresponding to an unwanted component from the
observation signals X.sub.n(t).
Other Means for Solving Problem and Effects of the Invention
[0024] In addition, in the photobiological measuring device
according to the present example, the above described computing
unit may have: an unwanted component removal mixing matrix making
unit for making an unwanted component removal mixing matrix in
which 0 is substituted for the column vector corresponding to an
unwanted component in the above described mixing matrix on the
basis of the independent component signal corresponding to an
unwanted component found in the above described unwanted component
signal determining unit; and an unwanted component removal
observation signal generating unit for generating unwanted
component removal observation signals by multiplying an unwanted
component removal mixing matrix with independent component
signals.
[0025] In the photobiological measuring device according to the
present example, the unwanted component removal mixing matrix
making unit first makes an N.times.N unwanted component removal
mixing matrix by substituting 0 for the column vector corresponding
to an unwanted component in the N.times.N mixing matrix on the
basis of the independent component signal S.sub.n(t) corresponding
to an unwanted component found in the unwanted component signal
determining unit. For example, when the power spectrum
S.sub.1(.lamda..sub.1) is not less than the threshold T, an
unwanted component removal mixing matrix is made by substituting 0
for the first column vector.
[0026] Next, as shown in the following formula (2), the unwanted
component removal observation signal generating unit multiplies the
N.times.N unwanted component removal mixing matrix by the N
independent component signals S.sub.n(t) in order to generate N
unwanted component removal observation signals X.sub.n'(t).
[ Formula 2 ] ( X 1 ' ( t ) X 2 ' ( t ) X n ' ( t ) ) Removal
Observation Signal Unwanted Component = ( 0 a 12 a 1 n 0 a 22 a 2 n
0 0 a n 2 a nn ) Removal Mixing Matrix Unwanted Component ( S 1 ( t
) S 2 ( t ) S n ( t ) ) Component Signal Independent ( 2 )
##EQU00002##
[0027] As described above, the photobiological measuring device
according to the present example can generate unwanted component
removal observation signals X.sub.n'(t) by removing the signals
corresponding to an unwanted component from the observation signals
X.sub.n(t).
[0028] In addition, in the photobiological measuring device
according to the present example, the above described predetermined
frequency band may be at least one frequency band selected from the
group consisting of a frequency band indicating the blood flow in
the skin, a frequency band indicating fluctuations in the heart
rate, and a frequency band indicating pulsation or respiration.
[0029] Furthermore, the analysis method according to the present
invention is an analysis method for generating an unwanted
component removal observation signal by removing the signal
corresponding to an unwanted component from an observation signal
using a photobiological measuring device having: a light
transmitting/receiving unit having a number of light transmitting
probes to be provided on the surface of the skin of a subject and a
number of light receiving probes to be provided on the surface of
the skin; and a light transmitting/receiving unit control unit for
acquiring an observation signal indicating chronological variations
concerning a portion to be measured in a subject by allowing the
above described light transmitting probes to irradiate the surface
of the skin with light while controlling the above described light
receiving probes in order to detect light emitted from the surface
of the skin, the analysis method having; a mixing matrix making
step of separating observation signals into the products of a
mixing matrix and independent component signals through independent
component analysis; and a unwanted component signal determining
step of finding the independent component signal corresponding to
an unwanted component from among independent component signals by
comparing the power spectrum in a predetermined frequency band in
each transformed independent component signal with a threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a block diagram showing the structure of the
photobiological measuring device according to one embodiment of the
present invention;
[0031] FIG. 2 is a plan diagram showing the positional
relationships between 16 light transmitting probes and 16 light
receiving probes in a holder;
[0032] FIG. 3 is a diagram showing a monitor screen displayed on
the photobiological measuring device according to the present
invention;
[0033] FIG. 4 is another diagram showing a monitor screen displayed
on the photobiological measuring device according to the present
invention; and
[0034] FIG. 5 is still another diagram showing a monitor screen
displayed on the photobiological measuring device according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] In the following, the embodiments of the present invention
are described in reference to the drawings. Here, the present
invention is not limited to the following embodiments, but of
course includes various modifications as long as the gist of the
present invention is not deviated from.
[0036] FIG. 1 is a block diagram showing the structure of the
photobiological measuring device according to one embodiment of the
present invention. In addition, FIG. 2 is a plan diagram showing
the positional relationships between 16 light transmitting probes
and 16 light receiving probes in a holder (light
transmitting/receiving unit).
[0037] Furthermore, FIGS. 3 to 5 are diagrams showing a monitor
screen displayed on the photobiological measuring device according
to the present invention. FIG. 3 shows a monitor screen of the
photobiological measuring device displaying 52 observation signals
X.sub.n(t), FIG. 4 shows a monitor screen of the photobiological
measuring device displaying 52 independent component signals
S.sub.n(t) and the transformed independent component signals
S.sub.n(.lamda.), and FIG. 5 shows a monitor screen of the
photobiological measuring device displaying 52 unwanted component
removal observation signals X.sub.n'(t). The photobiological
measuring device 1 is formed of a holder 11, a light emitting unit
2, a light detecting unit 3 and a control unit (computer) 20 for
controlling the entirety of the photobiological measuring device
1.
[0038] As shown in FIG. 2, the holder 11 has 16 light transmitting
probes 12 and 16 light receiving probes 13 in such a manner that
the light transmitting probes 12 and the light receiving probes 13
are arranged alternately in the longitudinal and lateral
directions. Here, the distance between the light transmitting
probes 12 and the light receiving probes 13 is 30 mm. In addition,
the 16 light transmitting probes 12 emit light while the 16 light
receiving probes 13 detect the amount of light (light detection
signal).
[0039] The light emitting unit 2 transmits light to one light
transmitting probe 12 selected from among the 16 light transmitting
probes 12 by the drive signal inputted from the computer 20. The
above described light is near-infrared rays (for example, 780 nm
and 850 nm).
[0040] The light detecting unit 3 individually detects
near-infrared rays (for example, 780 nm and 850 nm) received by the
16 light receiving probes 13, and thus outputs the 16 light
detection signals to the computer 20. The computer 20 is provided
with a CPU 21 and connects to a memory 25, a display 23 having a
monitor screen 23a, and a keyboard 22a and a mouse 22b, which are
input devices 22.
[0041] For the sake of description, the functions processed by the
CPU 21 can be divided into blocks: a light transmitting/receiving
unit control unit 4 for acquiring observation signals X.sub.n(t) by
controlling the light emitting unit 2 and the light detecting unit
3; and a computing unit 5 for generating unwanted component removal
observation signals X.sub.n'(t). Furthermore, the computing unit 5
has a mixing matrix making unit 51, a power spectrum computing unit
52, an unwanted component signal determining unit 53, an unwanted
component removal mixing matrix making unit 54 and an unwanted
component removal observation signal generating unit 55.
[0042] Furthermore, the memory 25 has a light detection signal
storage area 61 for storing light detection signals and a threshold
storage area 62 for storing predetermined frequency bands
.lamda..sub.1 and thresholds T.
[0043] The light transmitting/receiving unit control unit 4 has a
light emission control unit 42 for outputting a drive signal to the
light emitting unit 2, a light detection control unit 43 for
storing a light detection signal in the light detection signal
storage area 61 when the light detection signal is inputted from
the light detecting unit 3, and an observation signal generating
unit 44 for generating observation signals X.sub.n(t) which
indicate chronological variations in the concentration of
oxygenated hemoglobin.
[0044] The light emission control unit 42 controls the drive signal
for transmitting light to the light transmitting probes 12 so that
the drive signal is outputted to the light emitting unit 2.
[0045] The light detection control unit 43 controls 16 light
detection signals detected from the 16 light receiving probes 13 so
that the light detection signals are stored in the light detection
signal storage area 61 when a light detection signal is inputted
from the light detecting unit 3. That is to say, whenever light is
transmitted from one light transmitting probe 12, 16 light
detection signals are stored in the light detection signal storage
area 61.
[0046] The observation signal generating unit 44 acquires 52 light
detection signals, which are stored in the light detection signal
storage area 61 and transmitted from a light transmitting probe 12
to the adjacent light receiving probes 13, and generates
observation signals X.sub.n(t) indicating chronological variations
in the concentration of oxygenated hemoglobin on the basis of the
acquired 52 light detection signals.
[0047] That is to say, the light detection signals for light from a
light transmitting probe 12 to adjacent light receiving probes 13
are regarded as light detection signals gained from portions of the
brain to be measured #1 to #52, and therefore after light is
transmitted from all the light transmitting probes 12, 52 light
detection signals selected from 256 light detection signals are
gained. Then, on the basis of the thus-gained 52 light detection
signals, the concentrations of oxyhemoglobin (observation signals)
X.sub.n(t) in the 52 portions on the surface of the brain (#1 to
#52) are found (n=1, 2 . . . 52). As a result, as shown in FIG. 3,
52 observation signals X.sub.n(t) (#1 to #52) can be gained.
[0048] As shown in the formula (1), the mixing matrix making unit
51 separates the 52 observation signals X.sub.n(t) into the
products of a 52.times.52 mixing matrix and 52 independent
component signals S.sub.n(t) through independent component analysis
(mixing matrix making step).
[0049] The power spectrum calculating unit 52 Fourier transforms 52
independent component signals S.sub.n(t), which are functions of
time and intensity, so as to generate 52 transformed independent
component signals S.sub.n(.lamda.), which are functions of
frequency and intensity, and thus calculates the respective power
spectra of a predetermined frequency band .lamda..sub.1 in each
transformed independent component signal S.sub.n(.lamda.). As a
result, as shown in FIG. 4, 52 independent component signals
S.sub.n(t) and transformed independent component signals
S.sub.n(.lamda.) are gained (#1 to #52).
[0050] The unwanted component signal determining unit 53 compares
the power spectrum in the predetermined frequency band
.lamda..sub.1 in each transformed independent component signal
S.sub.n(.lamda.) with the threshold T, respectively, and finds the
independent component signal S.sub.n(t) corresponding to an
unwanted component from among the 52 independent component signals
S.sub.n(t) (unwanted component signal determining step). When the
power spectrum S.sub.1(.lamda..sub.1) is not less than the
threshold T, for example, the independent component signal
S.sub.1(t) is determined to be the signal corresponding to an
unwanted component. Meanwhile, when the power spectrum
S.sub.1(.lamda..sub.1) is less than the threshold T, the
independent component signal S.sub.1(t) is determined to be a
signal on the basis of the blood flow according to the brain
function. In addition, when the power spectrum
S.sub.2(.lamda..sub.2) is not less than the threshold T, the
independent component signal S.sub.2(t) is determined to be the
signal corresponding to an unwanted component. Meanwhile, when the
power spectrum S.sub.2(.lamda..sub.2) is less than the threshold T,
the independent component signal S.sub.2(t) is determined to be a
signal on the basis of the blood flow according to the brain
function. Thus, the independent component signals S.sub.n(t)
corresponding to the unwanted components are found from among the
52 independent component signals S.sub.n(t).
[0051] The unwanted component removal mixing matrix making unit 54
makes an unwanted component removal mixing matrix by substituting
zero for the column vector corresponding to the unwanted component
in the mixing matrix on the basis of the independent component
signals S.sub.n(t) corresponding to the unwanted components found
by the unwanted component signal determining unit 53. When the
power spectrum S.sub.1(.lamda..sub.1) is not less than the
threshold T, for example, an unwanted component removal mixing
matrix is made by substituting 0 for the first column vector. In
addition, when the power spectrum S.sub.2(.lamda..sub.1) is not
less than the threshold T, an unwanted component removal mixing
matrix is made by substituting 0 for the second column vector.
Thus, an unwanted component removal mixing matrix is made.
[0052] As shown in the formula (2), the unwanted component removal
observation signal generating unit 55 multiplies the unwanted
component removal mixing matrix by 52 independent component signals
S.sub.n(t) in order to generate 52 unwanted component removal
observation signals X.sub.n'(t). As a result, as shown in FIG. 5,
52 unwanted component removal observation signals X.sub.n'(t) (#1
to #52) are gained.
[0053] As described above, the photobiological measuring device 1
can generate unwanted component removal observation signals
X.sub.n'(t) by removing signals corresponding to an unwanted
component from the observation signals X.sub.n(t). Accordingly, the
observer, such as a doctor, can observe the unwanted component
removal observation signals X.sub.n'(t) in order to easily diagnose
whether or not there is a condition such as cerebral ischemia.
Other Embodiments
[0054] Though a holder 11 having 16 light transmitting probes 12
and 16 light receiving probes 13 is provided in the above described
photobiological measuring device 1, the holder may have a different
number of light emitting probes and light receiving probes, for
example, 12 light emitting probes and 12 light receiving
probes.
[0055] The present invention can be applied to an optical
encephalographic device for measuring the function of a portion of
the brain in a non-invasive manner using near-infrared rays (fNIRS:
functional near-infrared spectroscope), or an oxygen monitor for
monitoring the amount of oxygen consumption in the portion to be
measured in a living body.
* * * * *